1. Field of the Invention
The present invention relates to a water base pigment ink for ink-jet recording and an ink-jet recording apparatus which accommodates the same.
2. Description of the Related Art
In the ink-jet recording system, ink droplets are formed by a variety of ink discharge method including, for example, the electrostatic attraction method, a method in which mechanical vibration or displacement is applied to the ink with a piezoelectric element, and a method in which bubbles are generated by heating the ink to utilize the pressure generated thereby, and all or a part of the ink droplets are adhered to a recording objective such as paper to perform the recording.
The ink for ink-jet recording, which is used for the ink-jet recording system as described above, includes those in which various water-soluble dyes or pigments are dissolved or dispersed in a liquid medium composed of water and a water-soluble organic solvent. The water-soluble dye and the pigment may be compared with each other as follows. That is, the water-soluble dye is inferior in water resistance of recorded matters because of such a property that the water-soluble dye is dissolved in water, and the water-soluble dye is also greatly inferior in light resistance as compared with the pigment due to its chemical structure. On the other hand, the pigment is satisfactory in water resistance of recorded matters as compared with the water-soluble dye, because the pigment is water-insoluble. Therefore, in recent years, the changeover is progressively effected for the ink for ink-jet printer from the water-soluble dye ink to the pigment ink.
Nowadays, the recording quality, which is equivalent to those of photographic images, is required for the ink-jet printer. In order to satisfy such a demand, it is necessary for the recorded matter that the blurring on the paper surface including, for example, the feathering and the bleeding is restricted as less as possible, and the contour of the image is sharp. In general, a permeating agent is added to the ink for ink-jet recording in order to avoid the blurring. The permeating agent functions to quickly permeate the ink for ink-jet recording into the paper. As a result, it is possible to reduce the feathering and the bleeding. In this specification, the feathering refers to the fine blurring of the ink caused when the recording is performed with the ink of one color, and the bleeding refers to the blurring caused at the boundary between different colors when the color recording is performed with the inks of two or more colors.
Glycol-based n-butyl ether is known as permeating agents which are preferably selected for the water base ink for ink-jet recording from the permeating agents as described above. The glycol-based n-butyl ether includes, for example, ethylene glycol n-butyl ether, diethylene glycol n-butyl ether, triethylene glycol n-butyl ether, propylene glycol n-butyl ether, dipropylene glycol n-butyl ether, and tripropylene glycol n-butyl ether. However, when the glycol-based n-butyl ether is used for the water base pigment ink for ink-jet recording in which the pigment is used as the coloring agent, a problem has arisen such that the feathering and the bleeding cannot be sufficiently reduced.
The present invention has been made in order to solve the problem as described above, an object of which is to provide a water base pigment ink for ink-jet recording with which the feathering and the bleeding can be reduced, and an ink-jet recording apparatus which accommodates the same.
According to a first aspect of the present invention, there is provided a method for producing an ink for ink-jet recording, comprising preparing a dispersion of a pigment; preparing an ink solvent containing a water-soluble organic solvent and glycol ether; and mixing the pigment dispersion and the ink solvent; wherein amounts of respective components for constituting the pigment dispersion and the ink solvent are adjusted so that an Rf value, which represents a rate of flow of the pigment obtained when the pigment dispersion is developed with the ink solvent by paper chromatography, is not more than 0.5. According to the method for producing the ink of the present invention, the amounts of addition of the pigment dispersion and the ink solvent are established so that the Rf value, which represents the rate of flow of the pigment obtained when the pigment dispersion is developed with the ink solvent by paper chromatography, is not more than 0.5. On condition that the Rf value of the rate of flow is not more than 0.5, the pigment particles tend to stay at the place on the paper surface onto which the ink has been jetted, because the permeation speed of the ink into the paper is fast. As a result, it is possible to provide the ink with which the blurring such as the feathering and the bleeding can be suppressed.
According to a second aspect of the present invention, there is provided an ink for ink-jet recording comprising a dispersion of a pigment; a water-soluble organic solvent; and at least one glycol ether selected from the group consisting of ethylene glycol propyl ether, diethylene glycol propyl ether, triethylene glycol propyl ether, propylene glycol propyl ether, dipropylene glycol propyl ether, and tripropylene glycol propyl ether; wherein an Rf value, which represents a rate of flow of the pigment obtained when the pigment dispersion is developed by paper chromatography with a mixture liquid containing constitutive components of the ink except for the pigment dispersion, is not more than 0.5.
According to a third aspect of the present invention, there is provided an ink-jet recording apparatus comprising an ink-jet head; an ink tank which accommodates an ink to be supplied to the ink-jet head; and the ink of the present invention which is accommodated in the ink tank. When an image is formed by using the recording apparatus which accommodates the ink of the present invention, especially an ink set (ink cartridge), it is possible to suppress the blurring such as the feathering and the bleeding. The ink tank may be an ink container fixedly provided in the apparatus or an ink cartridge which is replaceable.